Endless unhappiness for skinflint (5)
I believe the answer is:
miser
'skinflint' is the definition.
(synonyms)
'endless unhappiness' is the wordplay.
'endless' means to remove the last letter.
'unhappiness' becomes 'misery' (misery is a kind of unhappiness).
'misery' with its last letter taken off is 'MISER'.
'for' is the link.
(Other definitions for miser that I've seen before include "not a spendthrift" , "Pinchpenny" , "Money-grubber" , "Skinflint, like Scrooge" , "One sparing with money" .)